Search results for "POWER"
showing 10 items of 5099 documents
Resistivity and irreversibility line of (Hg0.9Re0.1)Ba2CaCu2O6+δ HTS thin films
2003
Abstract High-quality epitaxial (Hg 0.9 Re 0.1 )Ba 2 CaCu 2 O 6+ δ HTS thin films were successfully prepared by pulsed laser deposition (PLD) of Hg-free precursor material on (1 0 0)-oriented SrTiO 3 substrates with subsequent Hg vapour annealing. (Hg 0.9 Re 0.1 )Ba 2 CaCu 2 O 6+ δ HTS thin films exhibit sharp superconducting transitions at T c ≈122 K. The electrical resistance for c -axis oriented HgRe-1212 films has been studied as a function of temperature and dc magnetic fields up to 10 T parallel to the crystallographic c -axis. The irreversibility line for the HgRe-1212 has been deduced from the data and investigated as a function of reduced temperature T / T c . The result of the irr…
Microwave electrodynamics of the antiferromagnetic superconductor GdBa2Cu3O7−δ
1999
The temperature dependence of the microwave surface impedance and conductivity are used to study the pairing symmetry and properties of cuprate superconductors. However, the superconducting properties can be hidden by the effects of paramagnetism and antiferromagnetic long-range order in the cuprates. To address this issue we have investigated the microwave electrodynamics of GdBa_2Cu_3O_{7-\delta}, a rare-earth cuprate superconductor which shows long-range ordered antiferromagnetism below T_N=2.2 K, the Neel temperature of the Gd ion subsystem. We measured the temperature dependence of the surface resistance and surface reactance of c-axis oriented epitaxial thin films at 10.4, 14.7 and 17…
Tunneling spectroscopy of giant vorticity states in superconducting micro- and nanorings at ultra-low temperatures
2008
Abstract When a superconducting contour is exposed to a magnetic field screening currents are induced. At temperatures well below the critical temperature Tc periodicity of the persistent currents can significantly exceed the superconducting flux quantum h / 2 e due to formation of metastable energy states with high quantum winding numbers (vorticity). We have studied the effect in normal metal-insulator-superconductor (NIS) and SIS’IS tunnel structures with the superconducting (S or S′) electrode in a shape of a loop. The tunnel current oscillates due to the modulation of the superconducting density of states by the persistent currents reaching the sub-critical values. In the limit of loop…
Normal and mixed state Hall effect in (Hg0.9Re0.1)Ba2CaCu2O6+δ fully textured HTSC thin films
2004
Abstract Temperature and magnetic field dependence of the Hall effect in the normal and mixed state of fully textured (Hg0.9Re0.1)Ba2CaCu2O6+δ (HgRe-1212) HTSC thin films prepared by laser ablation deposition have been studied. The longitudinal resistivity ρxx and Hall resistivity ρyx of HgRe-1212 superconductor thin films were measured for a wide range of magnetic fields from 125 mT to 12 T with the field perpendicular to the ab plane and the current in the ab plane. A sign change of the Hall resistivity is observed in fields below 3 T in the region close to the superconducting onset temperature. The temperature dependencies ρxx ∝ T and ρyx ∝ 1/T have been observed for HgRe-1212 thin films…
Probing the superconducting state of UPd2Al3 thin films by tunneling spectroscopy
1997
Abstract Giaever-type planar cross junctions of thin films of the heavy fermion superconductor UPd2Al3 and counter-electrodes of Au, Ag and Al were prepared. Tunneling barriers consisting of the native oxide layer of UPd2Al3 and artificial barriers of AlOx and UOx were investigated. The junctions without artificial barrier show a lack of reproducebility. On some junctions a BCS-like tunneling conductivity with a ratio of 2Δ 0 /k B T c ⋍ 3.8 was observed. Using oxidized Al deposited at room temperature as a barrier no substantial increase of the junction resistance occured. With Uraniumoxide a much higher resistance was obtained, but an association of the bias dependent junction conductivity…
Vortex-system ordering during magnetisation measurements in YBa2Cu3O7−δ films at low temperatures
2007
Abstract Zero-field-cooling dc magnetisation relaxation measurements performed on optimally doped epitaxial YBa 2 Cu 3 O 7− δ films with the external magnetic field H oriented parallel to the c -axis reveal the ordering of the creeping vortex-system in the low temperature T domain, due to the macroscopic currents induced in the sample. This dynamic ordering manifests itself through the appearance of a maximum in the T variation of the normalised vortex-creep activation energy. The location of this maximum in the H – T plane describes a well-defined current induced order–disorder line. Our results suggest the absence of a static elastic vortex glass in disordered high-temperature superconduc…
Vortex motion in Nb/PdNi/Nb trilayers: new aspects in the flux flow state
2011
We study the dynamics of vortex lines in Supercondutor/Ferromagnet/Superconductor (SFS) heterostructures at microwave frequencies. We have employed swept-frequency, Corbino-disk and resonant, dielectric-resonator techniques to obtain the field and temperature dependence of the vortex-state parameters. We concentrate here on the genuine flux-flow resistivity $\rho_{ff}$, that we access at subcritical currents using a sufficiently high driving frequency. We find that $\rho_{ff}$ does not follow the well-known Bardeen-Stephen model. Instead, it is well described by a full time-dependent Ginzburg-Landau expression at very thin F layer thickness, but changes to a previously unreported field-depe…
Relation between microstructure and transport properties of epitaxial YBa2Cu3O7-d thin films.
1997
Abstract In order to understand the origin of the high critical current densities observed in thin superconducting films compared to single crystals we measured in several epitaxial YBa 2 Cu 3 O 7−δ thin films the magnetic field and temperature dependence of the superconducting current density j s and the dynamical relaxation rate Q ≡ d ln j s / d ln( d B/ dt ). For all samples we found that (i) the superconducting current density j s is independent of magnetic field up to a certain field B Φ . The value of this field, which is sample dependent, decreases with increasing temperature; (ii) for fields B>B Φ , the superconducting current density falls off as B −1/2 over several decades; (iii) …
Shift of the surface-barrier part of the irreversibility line due to columnar defects in Bi2Sr2CaCu2O8 thin films
2003
We report the results of studying the influence of the uranium-ion irradiation of the Bi_2Sr_2CaCu_2O_8 thin films on the high-temperature part (close to critical temperature) of their irreversibility line. We studied irreversible properties of the films by measuring the hysteresis of nonresonant microwave absorption. The results have revealed the shift of irreversibility line towards low temperatures and magnetic fields. The effect is most significant for the films irradiated with large doses, more than 1T. This fact is in good agreement with the theoretical prediction by Koshelev and Vinokur of suppression of surface barrier by columnar defects.
Origin of the fast magnetization relaxation at low temperatures in HTS with strong pinning
2010
The temperature T variation of the normalized magnetization relaxation rate S in high-temperature superconductors (HTS) with strong vortex pinning exhibits a maximum in the low-T range. This was reported for various HTS, and the origin of the faster relaxation at low T appearing in standard magnetization relaxation measurements was usually related to specific pinning properties of the investigated specimens. Since the observed behaviour seems to be characteristic to all HTS with enhanced pinning (generated by random and/or correlated disorder), we show that the S(T) maximum can be explained in terms of classic collective vortex creep. The influence of thermo-magnetic instabilities in the lo…